string shorten: Don't produce output with --quiet

This would've printed stuff in case it didn't have to shorten (which
means it "failed" because the logic is "did something").

Fixes #12732

src/builtins/string/shorten.rs

@@ -166,8 +166,11 @@ fn handle(
 
                     pos += skip_escapes(&line, pos).max(1);
                 }
-                if self.quiet && pos != 0 {
-                    return Ok(());
+                if self.quiet {
+                    if pos != 0 {
+                        return Ok(());
+                    }
+                    continue;
                 }
 
                 let output = match pos {
@@ -215,8 +218,11 @@ fn handle(
                 }
             }
 
-            if self.quiet && pos != line.len() {
-                return Ok(());
+            if self.quiet {
+                if pos != line.len() {
+                    return Ok(());
+                }
+                continue;
             }
 
             if pos == line.len() {

tests/checks/string.fish

@@ -1064,6 +1064,14 @@ string shorten -m 2 foo
 string shorten -m 5 foobar
 # CHECK: foob…
 
+# Should produce no output and return false because there was nothing to shorten.
+string shorten -m 2 -q 12
+echo $status
+# CHECK: 1
+string shorten -lm 2 -q 12
+echo $status
+# CHECK: 1
+
 # Char is longer than width, we truncate instead.
 string shorten -m 5 --char ........ foobar
 # CHECK: fooba